The present invention relates to an actuator for a thrust reverser for an aircraft turbojet engine, more particularly such an actuator which will prevent retraction of a thrust reverser door from its opened, thrust reversing position in case of a malfunction in the safety locking mechanism which locks the thrust reverser in its closed, forward thrust position.
Thrust reversers for aircraft turbojet engines are, of course, well known in the art and serve to increase aircraft safety by providing a braking force to the aircraft when landing on wet or icy runways. Such thrust reversers may take the form of one or more thrust reversing doors pivotably attached to the engine nacelle which doors are movable between closed, forward thrust positions and open, reverse thrust positions. When in their opened positions, the doors redirect the gases from the turbojet engine to provide a reverse thrust to the aircraft.
In turbofan-type engines, wherein the turbojet engine drives a turbofan assembly, a significant portion of the thrust is achieved via the turbofan flow. Typically, such installations have an outer nacelle which encloses the turbofan and the turbojet engine so as to define a cold flow air duct between the exterior of the turbojet engine housing and the interior of the turbofan in the nacelle. In such engines having a high bypass ratio, it is known to apply the thrust reversers to only the cold flow duct to redirect a portion of the airflow passing through this duct.
A typical prior art installation is illustrated in FIGS. 1 and 2 wherein it can be seen that the structure comprises a forward, or upstream portion of the nacelle 1, one or more pivotable thrust reversing doors 2 and a stationary, downstream cowl 3. The forward or upstream portion 1 of the nacelle comprises an external nacelle panel 4 and an internal nacelle panel 5 which defines the exterior boundary of the gas flow duct, which panels are interconnected by support frame 6. Support frame 6 also supports the thrust reverser door actuator 7a which may comprise a hydraulic cylinder having an extendible and retractable piston rod so as to move the thrust reverser door 7 between its closed, forward thrust position (illustrated in FIG. 1) and its opened, reverse thrust position (as illustrated in FIG. 2). The number of thrust reverser doors 7 will depend upon the specific aircraft on which the nacelle is mounted and the location of the engine with respect to the remaining aircraft structure. FIG. 2 partially illustrates a turbojet engine nacelle having four thrust reverser doors 7, two of which are illustrated in the open, reverse thrust positions. An actuator 7 a may be operatively associated with each of the thrust reverser doors 7.
Typical examples of such known prior art thrust reversing systems may be found in U.S. Pat. Nos. 4,858,430; 4,916,895; 4,914,905; 4,976,466; 4,960,243; and 5,039,171.
As can be imagined, serious consequences may result from an untimely displacement of the thrust reverser to its opened, thrust reversing position should such occur at any time other than during landing when the aircraft is on the runway. Present day thrust reversers are equipped with many redundant systems to prevent such an occurrence. Typically, the thrust reverser doors are each fitted with a mechanical primary lock on the support structure and a mechanical secondary lock in the door actuator to prevent opening of the thrust reverser door in the event the primary mechanical lock should fail.
However, the secondary mechanical lock is typically internally located within the actuator and, should a malfunction in the secondary locking system occur, the thrust reverser door may operate in its normal fashion and hide the malfunctioning of the secondary mechanical lock. Thus, even the redundant safety locking systems have fallen short of avoiding all possible risks to safeguard against the simultaneous failure of the primary and secondary mechanical locks.
Some systems additionally have a further safety device to preclude any possible opening of the thrust reverser door by blocking any hydraulic fluid flow from the actuator when the thrust reverser door is in the closed, forward thrust position. Such a system is illustrated in European patent 0 524 875. However, this method entails a rather complex hydraulic system requiring additional means to protect portions of the thrust reverser hydraulic control system against over pressurization when in the locked mode. Furthermore, this safety device as in the internal mechanical system, itself may be subject to undetected malfunctions.